One of the biggest problems for young families is dividing up childcare duties. Women still get saddled with the bulk of the work, which can cause stress and undermine their careers. But many countries have found a solution to the problem: paternity leave. More freedom for men has meant more for women too.

While paid paternity leave may feel like an unexpected gift, the biggest beneficiaries aren't men, or even babies. In the long run, the true beneficiaries of paternity leave are women, and the companies and nations that benefit when women advance. In October, the World Economic Forum released its latest global gender-gap report, showing that countries with the strongest economies are those that have found ways to further women's careers, close the gender pay gap, and keep women—who in most nations are now better educated than men—tethered to the workforce after they become mothers. One strikingly effective strategy used by the highest-ranking countries is paternity leave, which, whatever else it may accomplish, is a brilliant and ambitious form of social engineering: a behavior-modification tool that has been shown to boost male participation in the household, enhance female participation in the labor force, and promote gender equity in both domains.

In Quebec, Canada, a 2006 program created a province-wide paternity leave that lasts 5 weeks. As a result, in 2010, 80 percent of fathers took paternity leave — up from 10 percent in 2001. This has created a new social norm, according to economist Ankita Patnaik, who has studied the Quebec program. She told Mundy that "families felt they were wasting something" when fathers didn't take time off. "Now dads might feel bad for not taking leave—your baby loses this time with parents." Interestingly, paternity leave sets household changes in motion that last for years.

According to Mundy:

The policy has achieved many of the hoped-for long-term outcomes, chief among them more fluidity in who does what around the house. Previous studies found that fathers who take paternity leave are more likely, a year or so down the road, to change diapers, bathe their children, read them bedtime stories, and get up at night to tend to them. Patnaik's study confirmed this; looking at time-use diaries, she found that men who were eligible for the new leave—whether or not they took it—ended up spending more time later on routine chores like shopping and cooking.

As a result, women felt that men were taking more responsibilities with childrearing and were less likely to suffer from depression. More importantly, they returned to their previous jobs in much higher numbers than they did before the 5-week paternity leave program. So the labor inside the home and outside is more evenly shared between the father and mother.

Paternity leave is a social experiment whose goals appear to have worked far better than anyone could have hoped.